There are many systems that use a current mirror as part of a circuit. A current mirror typically includes a pair of transistor devices coupled together such that the current through one of the devices matches, or mirrors the current in the other device. A current mirror is typically used as a current regulator.
A current mirror may have many applications, a particular application being in a power amplifier. A power amplifier may be used in a variety of devices including, for example, a cellular telephone or other portable wireless communication device. When employed as a power amplifier in a portable communication device, current mirrors provide bias for a series of amplification stages of the power amplifier. In order to enable each current mirror, a reference current is used to charge a capacitance associated with each current mirror. However, in many power amplification applications a large capacitance is desired to meet stability and noise performance of the power amplifier. Unfortunately, the large capacitance gives rise to a slow enable time because a relatively small current must charge a relatively large capacitance to the bias point of the current mirror before the current mirror if fully activated.
Therefore, it would be desirable to have a way of rapidly biasing a current mirror that has a relatively large capacitance.